Methane is an abundant gas emitted from both natural and anthropogenic sources. It is an excellent source of energy and heat via highly exothermic combustion. But from a biological perspective, methane also serves as a carbon and electron source for methane-utilizing bacteria (methanotrophs). Methanotrophs use methane as a sole or primary carbon source to mediate diverse natural processes including greenhouse gas mitigation, environmental remediation of pollutants and nitrogen cycling. In addition, methanotrophs are of great interest for their biotechnological applications. They can be used in biodiesel generation, propylene oxide production, single cell protein production, extracellular polysaccharides production, human health supplements production, and biological nitrogen removal. Also, researchers have developed methane-based poly(3-hydrobutyrate) (P3HB) biopolymer production processes using P3HB-accumulating methanotrophs (Type II methanotrophs).
An obstacle for methane-based bio-products, however, is the inefficient mass transfer of gases needed for high-density fermentations, as both methane and oxygen are sparingly soluble in the aqueous media used for methanotrophs growth. There is a strong connection between the rates of mass transfer, cell growth, and the production of desired products. To increase the mass transfer rates of sparingly soluble gases, bioreactors with vigorous mixing or agitation capabilities are typically used to create small gas bubbles that increase the gas-liquid interfacial area. The need for agitation inevitably increases the power demand and the operation cost. High shear rates from agitation can also damage cells and inhibit their growth.